diver2522

Hi all, I have a 2000 ls1, check engine light is on coming up as cylinder 2 misfire, changed injector, coil pack, plug, wire, compression test, checked for vacuum leaks, pulled valve cover off and everything looks fine, I'm out of ideas as to why it would still misfire, any help is greatly appreciated!

G Atsma

Intermittent or constant?

diver2522

Definitely misses at idle but seems to go away as your accelerating but misses again in 5th gear doing about 45 mph, car is jerky when under a small load, give it gas and seems to clear up

mintws6

When was the last time you changed O2 sensors? if it idles relatively fine on a cold start and as it warms up starts to miss that could be your problem.

Darth_V8r

iTrader: (4)

May need to do a leak down on #2 to verify it holds compression

diver2522

Didnt notice any loss of compression with a compression test, let it sit for at least 5 mins and no loss on the guage

diver2522

But no check engine light code for an o2 sensor? Only code that comes up is p0302, definitely starting to be a mystery since everything is changed on that cylinder

mintws6

I have had O2's fail and not throw a code. If they are old its just something I would check. Fairly easy to do.

Darth_V8r

iTrader: (4)

compression tester gauge won't show pressure loss. It's designed to capture so after the test you can read it. Leakdown is different.

diver2522

Ill try a leakdown test next I suppose, changed both upstream 02's today and still misfiring ugh

Darth_V8r

iTrader: (4)

Yeah. O2 sensor affects all four on a bank not just one. For it to affect only one cylinder, it is either fuel, spark, or loss of compression. Or something really dumb like a wad of tape plugging the intake runner (highly unlikely)

diver2522

By the time I find the misfire I'm hoping it is something dumb lol, I'm going to try to do the leakdown test this weekend, just boggles my mind with everything that I've changed on that cylinder and it still misses on that cylinder, if the leakdown test goes good, then I'm totally lost lol

mintws6

If this problem is intermittent like you are saying then it couldn't be leak by right? like that would be constant I think it has to do with fuel if you checked your injectors, plugs and coils then I would check the O2's. Even if they are brand new sensors I've had them go bad. Does the car idle on cold start fine? and when it warms up starts to miss? That would also point to O2 sensors. Other thing would be to check wire harness that goes to #2 and see if it got wet or some kind of damage to it? Just throwing out ideas. Hopefully you didn't reverse the harness or something weird??

mintws6

I do agree with Darth though usually the code thrown from O2 would be a random misfire code and not just one cylinder but heck ECU is weird sometimes.

Jays_SSZ28

iTrader: (2)

Can you take the spark plug out and post a good quality picture of it?

88bruce

Did you remove the intake manifold? A leaking intake manifold gasket will lean out the mixture
and cause a misfire at idle.

diver2522

I will do that sometime this week

diver2522

I never removed it, not sure if the previous owner ever removed it, would you maybe recommend spraying some throttle body cleaner around the gasket area? I've done it before and heard no change in the idle at all but can try it again

88bruce

There are eight separate intake manifold gaskets on the LS1, so it's possible just one could go bad.
Since #2 cylinder is on a corner, the intake manifold bolts may need to be retorqued.

Edit: Just to clarify, I'm not referring to the throttle body gasket. The intake manifold gaskets seal
the intake manifold to the ports on the cylinder heads. There are ten bolts attaching the intake manifold
to the engine.

Darth_V8r

iTrader: (4)

If your heads have been ported, it is also possible oil is leaking past the rocker bolt into the runner and oil-fouling the plug